SMALL DAMS PETITS BARRAGES

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Fig. 7.16 – Example of sliplining – insertion of plastic (high density polyethylene) pipe into larger diameter concrete pipe (from FEMA, 2005) Need filter at downstream when sliplining Seepage before slipliner Seepage after slipliner (without filter) (with filter) Filter diaphragm Fig. 7.17 – Possible effect of a slip-liner on pore pressure in an embankment dam, illustrating the need for a downstream filter diaphragm (courtesy of Maryland (USA) Dam Safety Division) 7.3.6.2 Filter Around Conduits Filters are generally accepted as the preferred method to protect against seepage or leakage around the outside of conduits that penetrate the dam or its foundation. Use of antiseep (cutoff) collars on conduits is no longer considered acceptable practice due to the high incidence of historic failures attributed to poor compaction control around these protrusions on the conduits. Filters used in conjunction with conduits generally fall under three categories: chimney filters, filter diaphragms, and filter collars. Detailed design recommendations for filters around conduits are provided in FEMA (2005), and some key points are summarized in this section. 134
Embankment dams that have properly designed and constructed chimney filters normally do not require a separate filter zone to control seepage around the outlet conduit. When full hydraulic height filters are installed as a seepage remedy for the embankment (see Figure 7.16 and Figure 7.17, for example), care should be taken to incorporate the filter zone around the outlet conduit as well. A filter diaphragm is a zone of engineered filter sand placed around the conduit to specified dimensions. The dimensions shown in Figure 7.18 are based on guidance provided by NRCS (1989, 1990). Normally a minimum width of 1 m around the conduit is provided. Other details for positioning and designing filter diaphragms are provided in FEMA (2005). Filter diaphragms are economical and effective seepage rehabilitation features that can be incorporated on dam embankments that do not have chimney filters, or which may have defective filter zones. Fig. 7.18 – Typical configuration of a filter diaphragm for conduits through embankment dams (after FEMA, 2005; NRCS 1989, 1990) A filter collar is a zone of filter material (typically sand) that completely surrounds a specified length of the outlet conduit. The lateral dimensions beyond the outside of the conduit are limited in extent compared to a filter diaphragm. It is recommended that filter collars be used only for special conditions when the only seepage considered likely is flow around the periphery of the pipe, and soil conditions are less conducive to erosion. Sometimes it is difficult to construct the collar in the “downstream zone” of an embankment when the reservoir is full, or partially full. In such cases the conduit pipe can be lengthened and covered with a berm of soil on the downstream side of the dam. Special attention must be paid to the control valve at the downstream end of the existing outlet pipe if it is to be left in place “as a spacer” so that sufficient space is added for the connection by bolts. 7.3.6.3 Pipe Abandonment Outlet pipe must sometimes be abandoned, such as where the conduit has deteriorated to the point that it is no longer safe to operate. It is often considered technically and economically more feasible to abandon the conduit in place, rather than excavate and remove it. If it is necessary for an “abandoned conduit” to remain in place in the dam or its foundation, the conduit must filled with grout. A filter diaphragm should be installed around the grouted 135
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SMALL DAMS Design, Surveillance and
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FOREWORD The ICOLD - International
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ACKNOWLEDGEMENT The Ad Hoc Committe
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FOREWORD ACKNOWLEDGEMENT SUMMARY TA
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5.5.5 Compaction in confined areas
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7.2.1 Introduction 7.2.2 Spillway c
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1. SMALL DAMS DEFINITION AND CLASSI
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2 Fig. 1.2 - Relationship H . V wit
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1.3 REFERENCES [1] French Committe
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2.3 ZONED EARTHFILL DAMS In arid pa
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sloping core guarantees water impou
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Fig. 2.11 - Hlinky Concrete Gravity
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Fig. 2.13 - Photograph of Neusberg
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The gabion dam as the gabion retain
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Some inflatable dams are operated b
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3.1 INTRODUCTION 3. SAFETY OF SMALL
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Condition Effect on safety 13. Dama
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Fig. 3.2 - Massive dam break overto
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and suffusion or internal instabili
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downstream part of the embankment m
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small dam impounding a lot of water
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Whenever the Supervising Authority
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emergency management organizations
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c) The decommissioning plan should
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5.1 INTRODUCTION 5. FEATURES OF THE
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5.2 DESIGN FLOODS Inadequate flood
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downstream slope will show seepage
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Fig. 5.2 - Design Freeboard 5.4.3 F
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2 U f Fe S 1400 D Where Uf is the d
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Maximum compaction is obtained at c
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characteristic must be determined.
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5.6.1 Foundation Watertightness The
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� A continuous vertical chimney d
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Thickness of pervious layer Thick D
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t 5.7.1.4 Practical Considerations
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It is generally accepted that cohes
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� Simple Bishop (1955) � Spence
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� The elements for surface draina
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The supporting layer for the rip-ra
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For very small reservoirs (fetch of
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The junction of the downstream slop
Page 83 and 84: Fig. 5.14 - Hongshiyan homogenous d
Page 85 and 86: material has been left in place or
Page 87 and 88: The homogeneous dam is recommended
Page 89 and 90: [3] OL and OH soils are not recomme
Page 91 and 92: part (core) lies in the zone (Fig.
Page 93 and 94: 6. GUIDELINES ON SURVEILLANCE OF SM
Page 95 and 96: cases the owner may retain the serv
Page 97 and 98: Surface displacement on an embankme
Page 99 and 100: Fig. 6.1 - Leakage measurement usin
Page 101 and 102: Water Level Sounder - Details of th
Page 103 and 104: pressure) Left abutment 2 5 Weir ga
Page 105 and 106: Fig. 6.9 - Recommended standpipe pi
Page 107 and 108: the others weir gauges need to be i
Page 109 and 110: � Earthquakes sensible at the dam
Page 111 and 112: APPENDIX INSPECTION CHECKLIST FOR S
Page 113 and 114: Exposed reinforcement � The condu
Page 115 and 116: These spillways can be lined or unl
Page 117 and 118: flowing water. Flowing water with h
Page 119 and 120: Fig. 7.3 - Installation of the arti
Page 121 and 122: Fig. 7.7 - Dam overtopping protecti
Page 123 and 124: complete construction was in 2001,
Page 125 and 126: In some cases, the downstream face
Page 127 and 128: Tube-a-manchettes injection system
Page 129 and 130: 7.3.5 Slope Protection Measures 7.3
Page 131 and 132: Pipe Rehabilitation SLIPLINING MODI
Page 133: Conditions Pros Cons Comments types
Page 137 and 138: and minimize erosion. Design of sui
Page 139 and 140: [20] SMEC- “Draft Guidelines for
Page 141 and 142: present visual information. It must
Page 143 and 144: Fig. 8.1 - Three small dams in casc
Page 145 and 146: Social Disruption low (rural area)
Page 147 and 148: Fig. 8.4 - Flood water level after
Page 149: 8.9 REFERENCES [1] BURREC (1994) -
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SMALL DAMS PETITS BARRAGES

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